Rawalpindi (Punjabi, Urdu: راولپنڈى‎, Rāwalpiṅḋī), commonly known as Pindi (Punjabi: پنڈی), is a city in the Punjab, Pakistan. It is the 4th most populous metropolitan area of Pakistan. The center of the Rawalpindi is only 14 kilometres (9 mi) from the center of Islamabad. Due to the high interdependence and intertwined areas of the two cities, they are known as the twin cities of Rawalpindi/Islamabad. In the 1950s, Rawalpindi's population was smaller than Hyderabad and Multan, but the city's economy received a boost during the building of Islamabad (1959–1969), during which Rawalpindi served as the national capital. Rawalpindi is in the northernmost part of the Punjab province, located 275 km (171 mi) to the north-west of Lahore. It is the administrative seat of the Rawalpindi District.